Brachytherapy needles, plugged with suppository material, bone wax or other bioabsorbable materials and then loaded with radioactive seeds, are known in the art. However there are numerous problems associated with loading and plugging the needles. Problems with the current art of plugging the distal end of a needle with a pre-shaped cylindrical plug stem from the fact that the plug does not exactly take on the inner shape of the needle as a liquid would. As needles are manufactured, the inside diameter (ID) has a plus/minus tolerance. In addition, pre-formed cylindrical plugs may also vary in size. As a result of these to variables in the needles and plugs, the fit between the needles and the plugs may be compromised which often causes a variable and therefore uncontrolled push out pressure or plug failure when the plug is ejected from the needle via a stylet. To overcome this issue, manufacturers have added mechanical “crutches” to aid in the retention of the plug such as indentations or “U” shaped tabs cut into the needle wall and protruding into the ID of the needle in the area the plug will be placed to compensate for this problem. The additional manufacturing complexities drive the production cost of the needle higher. Additionally, “U” shaped tabs do not prevent bodily fluids from traveling up the needle.
There are additional problems with the “one size fits all plug.” These plugs result in push out pressures that are not easily adjustable to the different needs in the market. The radioactive seeds, known as brachytherapy seeds, are often times prepared in a “strand”, inserted into a pre-plugged needle for implantation and expelled into the appropriate organ to be treated. The various stranding materials in the market are constructed differently and may jam in the needle if the operator of the needle has to apply too much pressure to release the plug.
Alternatives to preformed plugs are pliable bone wax plugs and molten liquids. However there are also several problems associated with the use of pliable bone wax and molten liquids. The plugging material not only sticks to the inside of the needle, but the outside as well, as the needle is “dipped” or pushed into a container of molten liquid or block of bone wax. This requires the assembler of the needle to “wipe” the exterior “clean” of the residual material. The length of bone wax plugs may also unpredictably vary. Additionally, oftentimes the configuration of seeds and spacers needs to be removed and repositioned. However, as the once loaded seeds are expelled from the needle, the seeds now have bone wax on them that has to be removed from the seeds prior to re-inserting them into a new needle for implantation. If the bone wax is not removed the seed will be very difficult to handle, sticking to the loading tool and the needle into which they are to be re-loaded. Seeds loaded into needles that are plugged, using the dipping method and molten suppository material having lower molecular weight PEG, will have the same issue due to the naturally sticky state of this material at room temperature. Lower molecular weight PEG formulations also will not retain their shape under the temperatures some times seen with sterilization (about 50° C.) as would PEG of higher molecular weights such as PEG 8000 for example. If the plug melts during the sterilization of the pre-loaded needle the seeds will fall out.